From DE 42 36 436 A1 a measurement method is known for the contact-free determination of the surface weight of thin material sheets using ultrasound. In this method, the transmission absorption of an ultrasonic beam emitted through a sheet material is determined using an ultrasonic transmitter and ultrasonic receiver. The surface weight is calculated using the absorption and a calibration factor.
From DE 201 09 119 U1 another apparatus for thickness measurement of material sheets is known. There, the material sheet is drawn over a roller and the thickness measurement is executed by a sensor mounted on a dolly which traverses back and forth over the roller.
There is a need for providing a method for improved calibration of a sensor. Furthermore, there is a need for providing an improved method or an improved apparatus for measurement of layer thickness and/or surface weight of a material sheet.